Present day packaging of electronic equipment frequently involves the soldering of electronic components and connectors containing solid state devices to an interconnection medium such as a printed circuit board. Where high density packaging is required, such as in the computer field, the fine detail of the interconnections on such circuit boards does not result in a sufficient quantity of solder around the terminal-receiving holes in the boards to insure a good solder connection. Accordingly, it has been expedient to place individual solder rings upon each terminal or solder-tail after they have been inserted through the corresponding holes in the printed circuit board and prior to the soldering operation. Since connectors may involve hundreds of terminals, the task of placing a ring on each is extremely laborious and time consuming.
In order to eliminate the problems associated with the handling of individual solder rings, present day practice has been to employ chains or strings of solder rings formed in a specified pattern matching that of the solder-tails of the device to be mounted on the board. However, this technique has produced an even more serious problem. Vapor phase condensation soldering, wherein all of the board soldering is accomplished simultaneously, is often preferred for the speed of the soldering operation and the relatively moderate temperatures utilized--the latter being non-damaging to the circuit boards. On the other hand, in condensation soldering, the instantaneous fusion of all of the rings in the patterned chain has resulted in erratic solder flow characteristics. That is, one or more molten rings may not remain at their respective locations, but may flow instead to other terminals being soldered if the flow path to the latter offers less resistance. This leaves some terminals with an excess of solder, and others, with insufficient solder to provide an adequate joint.
It is apparent from the foregoing considerations that while it is desirable to achieve simultaneous multiple placement of solder rings upon the terminals to be soldered in order to make the task less tedious and time consuming, it is necessary that a condensation soldering operation be able to be employed without detrimental effects. The present invention accomplishes these goals.